DESCRIPTION (adapted from the ABSTRACT): Mycobacterium spp. have gained prominence through frequent infections of individuals immunocompromised by the acquired immunodeficiency syndrome (AIDS) M. tuberculosis and M. avium have evolved to survive within the macrophage, a cell more usually associated with the eradication of invading microbes, an interaction that enables mycobacteria to avoid host defenses and poses problems for effective chemotherapy. Recent work in the Principal Investigator's laboratory has extended our appreciation of the intracellular compartment inhabited by these bacteria. The vacuoles have a high pH and are extremely dynamic, intersecting readily with the sorting/ recycling endosomal system of the host cell. However, despite the increase in our appreciation of this compartment, several key questions still remain, the most notable being how mycobacteria exert their influence over the phagosome and host cell. The Investigator describes approaches to address the following questions: (1) How do mycobacterial species prevent phagosome maturation? (2) How do activated macrophages overcome this suppression and kill the infecting microbe? (3) How do mycobacteria modulate their host cell and bystander macrophages to suppress localized cellular immune responses and so avoid macrophage activation? The new approaches to the questions represent novel procedures to exploit the newly emergent genome databases and mutagenesis protocols. The Investigator has applied his cell biology expertise to the development of genetic screens to isolate mutants deficient in different aspects of intramacrophage survival. The studies will proceed in close interaction with continued cell biological analysis of trafficking pathways into and out of mycobacterial vacuoles and transfer between infected macrophages and bystander cells. In addition, mutants defective in factors key to intramacrophage survival will be examined in mice for their potential as vaccines against MAC and M. tuberculosis. The results should enhance understanding of intracellular survival by M. tuberculosis and other pathogenic mycobacteria.